1. Field of the Invention
The present invention relates to an artificial kidney which allows purification of the blood in places such as the home or a travel destination, without imposing a particularly great burden on daily life, and without the need for patients suffering from renal insufficiency to attend hospital, and it relates to an insertion guide used therein.
2. Description of Related Art
It has been predicted that by the year 2000 there will be 1,000,000 patients suffering from renal insufficiency around the world, 200,000 of them in Japan alone.
Methods of therapy which are known at the present time include, by way of example, artificial dialysis, kidney transplant and continuous ambulant peritoneal dialysis, abbreviated to CAPD, in which dialysis is carried out using a membrane.
However, CAPD entails a high risk of inducing complications which have a poor prognosis such as sclerotic peritonitis due to bacteria which invade the abdominal cavity from the tube system. Also, although the kidney bank system is becoming more widespread, and kidney transplants are the most common form of organ transplant, the number of registered donors nevertheless falls far short of the number of aspirant patients. The majority of patients with renal insufficiency therefore have to rely on artificial dialysis.
In artificial dialysis, blood is extracted from an artery via a tube, the blood is led into a dialysis device known as a dialyzer, where it is purified, and the purified blood is put back into the body.
The dialyzer is provided on the inside with a dialysis membrane formed from a flat membrane, hollow fibres or the like, and is arranged in such a way that, when the blood flows through it, waste materials in the blood pass through the dialysis membrane and diffuse into a dialysis fluid which flows on the outside, and thus the contaminated dialysis fluid is discarded and the constituents of the now cleansed blood are adjusted before it is put back into a vein.
In this case, the blood is supplied to the artificial kidney at 200 cc/min, but, even so, it requires about 5 to 6 hours to purify the blood of the whole body.
Moreover, such dialysis has to be carried out at a frequency of 3 times a week, which is to say about once every 2 days, and the time constraints of dialysis impose a considerable burden on the daily lives of patients and substantially curtail the social activities of patients.
Artificial kidneys which allow dialysis in the home and elsewhere have therefore also been proposed, but some 150 to 200 liters of dialysis fluid is required in a single dialysis in order to continuously replace the contaminated dialysis fluid in the dialysis device with fresh fluid, and artificial kidneys have been of a large size. Also, the patient has obviously not been able to move away from the bed while receiving dialysis.
In healthy individuals, on the other hand, about 180 liters of blood are filtered by the glomeruli in the kidneys within 24 hours, of which between 1 and 2% is discharged outside the body and the remaining 98 to 99 per cent is reabsorbed. Here, the amount of filtration by the glomeruli is 125 cc/min, while the amount discharged outside the body is 2 cc/min.
Now, if the blood is led into a filtration device, an aqueous fraction including waste materials extracted and excreted at 2 cc/min, and a fresh replenishing fluid mixed with the blood from which the waste materials have been eliminated and made to flow back into the body at 2 cc/min, then the amount discharged outside the body will be on the same level as in a healthy individual, and 2 cc will be purified every minute, but the blood of dialysis patients contains large amounts of urea and other unwanted waste materials, and requires an elimination level of at least 10 times this.
A purification rate of 20 cc/min should be achieved in order to satisfy this requirement, it is sufficient to excrete 20 cc/min of the water fraction (initial urine) containing waste materials obtained by the filtration of the blood, and to put back 20 cc/min of fresh replenishing fluid, and filtration devices with such a capacity can now be reduced to a size such that they are portable.
However, this method requires 1.2 liters per hour, or approximately 30 liters per 24 hours, of fresh replenishing fluid, and, since the amount of replenishing fluid used is excessive, portability cannot be extended to the replenishing fluid even if the filtration device is rendered portable, and thus it cannot be employed in portable artificial kidneys, in addition to which it is still inconvenient even if put to use in the home.
Also, when blood is purified using an artificial kidney, the system is arranged such that the blood is made to flow into a circulatory system outside the body, where it is purified, and is then made to flow back into the body by the insertion of an arterial needle and a venous needle into a fistula formed in the arm.
Further, when the blood is purified in a place such as the home, the needles have to be inserted by the individual him or herself since there are no dedicated staff, and even individuals who are not skilled at performing the insertion have to be given an ability to insert the needles to a certain degree since dexterity of insertion affects the life of the fistula.
Thus, the technical problems for the present invention are, firstly, to provide an artificial kidney which does not require a large amount of dialysis fluid or replenishing fluid, and with which the blood can be purified even in places such as the home and travel destinations, and secondly to provide an insertion guide which allows anybody at all to easily insert the needles into the fistula formed in the arm when such an artificial kidney is used.
In above mentioned problem, an artificial kidney according to the present invention is characterized in that a circulation system outside the body connected to the circulation system inside the body is provided with a filtration device which filters blood taken from inside the body and extracts, in the form of initial urine, a water fraction containing waste materials; a distillation device which distills the above mentioned initial urine and recovers distilled water, and discharges the initial urine in which the waste materials have been concentrated; and a purified blood mixing device which uses the above mentioned distilled water to dilute a concentrated replenishing fluid to a predetermined concentration, and mixes it with the blood from which initial urine has been eliminated in the above mentioned filtration device and returns the mixture into the body.
When the artificial kidney according to the present invention is employed, the water fraction (initial urine) containing waste materials is extracted as a filtrate at about 30 cc/min by taking blood at about 125 cc/min from inside the body and filtering it in a filtration device.
Also, by using the distillation device to perform distillation and not discharging the filtrate straight away, 28 cc/min of distilled water is recovered, and the initial urine in which waste materials have been concentrated is discharged at 2 cc/min.
Also, approximately 124 cc/min of purified blood, obtained by mixing approximately 1 cc/min of a concentrated replenishing fluid diluted with 28 cc/min of distilled water, and 95 cc/min of blood from which initial urine has been eliminated in the filtering device, is returned to the body.
In this way, purification of the blood is possible with only a small amount of concentrated replenishing fluid since distilled water obtained from the distillation of initial urine is reused, and this distilled water is used to dilute the concentrated replenishing solution.
At this time, if a commercially available dialysis source fluid which has been concentrated 35 times is used as the concentrated replenishing solution, then the requisite amount of dialysis source fluid is 28/35=about 0.8 cc/min, and is 28xc3x9760xc3x9724/35=1152 cc even assuming that the artificial kidney is made portable and the blood is purified continuously over 24 hours, and thus, by way of example, it is sufficient to replace a bag containing 300 cc every 5 to 6 hours.
In this way, given that the blood filtration rate inside the body is 28 cc/min, it is possible to maintain a kidney performance approximately 25% of the filtration rate of 125 cc/min of healthy individuals, and this is believed to be on the same level as the kidney performance in patients undergoing dialysis in institutions such as dialysis centers attached to university hospitals and the like.
Further, in order to overcome the second problem, the insertion guide according to the present invention disclosed in claims 7 to 12 is characterized in that it is an insertion guide for inserting an arterial needle which takes blood out from the body, and a venous needle which returns purified blood into the body, into one or two fistulae formed in a vein running beneath the skin of the arm: said insertion guide has formed in it an arterial guide hole which guides the above mentioned arterial needle downwards at an incline from the shoulder side to the wrist side relative to the above mentioned fistula, and a venous guide hole which guides the above mentioned venous needle downwards at an incline from the wrist side to the shoulder side relative to the above mentioned fistula, running through a holder fitted to the arm in such a way as to cover the above mentioned fistula.
When the insertion guide according to the present invention is employed, once the holder has been fitted to the arm and the arterial needle and the venous needle have been poked through their respective guide holes, the arterial needle is inserted by being guided downwards at an incline from the shoulder side to the wrist side relative to the fistula, while the venous needle is inserted by being guided downwards at an incline from the wrist side to the shoulder side relative to the fistula.
The needles can be inserted simply and under more or less the same conditions whoever inserts them, without any lateral shaking, since they are guided only in the longitudinal direction by the guide holes, both when they are being put in and when they are being withdrawn.